Very Strong T[CLC]e[/CLC]V Emission as Gamma-Ray Burst Afterglows

Abstract

Gamma-ray bursts (GRBs) and following afterglows are considered to be produced by dissipation of kinetic energy of a relativistic fireball, and the radiation process is widely believed to be synchrotron radiation or inverse Compton scattering of electrons. We argue that the transfer of kinetic energy of ejecta into electrons may be an inefficient process and hence the total energy released by a GRB event is much larger than that emitted in soft gamma rays by a factor of ~(mp/me). We show that, in this case, very strong emission of TeV gamma rays is possible due to synchrotron radiation of protons accelerated up to ~1021 eV, which are trapped in the magnetic field of afterglow shocks and radiate their energy on an observational timescale of about a few days. This suggests the possibility that GRBs are most energetic in the TeV range, and such TeV gamma rays may be detectable from GRBs even at cosmological distances, i.e., z~1, by currently working ground-based telescopes. Furthermore, this model naturally gives a quantitative explanation for the famous long-duration GeV photons detected from GRB 940217. If TeV gamma-ray emission that is much more energetic than GRB photons is detected, it provides a strong evidence for acceleration of protons up to ~1021 eV.